Lipid extraction and esterification for microalgae-based biodiesel production using pyrite (FeS2)

• Pyrite can be used for lipid extraction as well as esterification processes.
• Microalgae cells can be effectively destroyed by the Fenton reaction using pyrite.
• Free fatty acids can be converted to biodiesel by pyrite under acidic condition.
• Two-step esterification process can solve the problem of alkaline catalyst.

In this study, pyrite (FeS2) was used for lipid extraction as well as esterification processes for microalgae-based biodiesel production. An iron-mediated oxidation reaction, Fenton-like reaction, produced an expected degree of lipid extraction, but pyrite was less effective than FeCl3 commercial powder. That low efficiency was improved by using oxidized pyrite, which showed an equivalent lipid extraction efficiency to FeCl3, about 90%, when 20 mM of catalyst was used. Oxidized pyrite was also employed in the esterification step, and converted free fatty acids to fatty acid methyl esters under acidic conditions; thus, the fatal problem of saponification during esterification with alkaline catalysts was avoided, and esterification efficiency over 90% was obtained. This study clearly showed that pyrite could be utilized as a cheap catalyst in the lipid extraction and esterification steps for microalgae-based biodiesel production.